In an electrophotographic (EP) imaging process used in printers, copiers and the like, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over an outer surface. An electrostatic latent image is formed by selectively exposing the uniformly charged surface of the photosensitive member. Toner particles are applied to the electrostatic latent image, and thereafter the toner image is transferred to the media intended to receive the final permanent image. The toner image is fixed to the media by the application of heat and pressure in a fuser assembly. A fuser assembly may include a heated roll and a backup roll forming a fuser nip through which the media passes. A fuser assembly may also include a fuser belt and an opposing backup member, such as a backup roll.
Traditionally, the fuser rolls and belts comprise an outer compliant layer. These compliant layers can be deformed permanently, i.e., compression set, if left inactive and under pressure for prolonged periods of time. The deformation can lead to print defects.
U.S. Pat. No. 6,253,046 discloses a fuser assembly comprising hot and backup rolls. A fuser roll nip release mechanism is provided for relieving a pressure between the rolls during non-use of the fuser assembly. A feedback system comprising one or more sensors in combination with a controller is used to control the position of the nip release mechanism and, hence, the hot and backup rolls.
It would be desirable to have a nip release mechanism not requiring a sensor feedback system so as to reduce the cost of the mechanism.